The present invention relates to apparatus for measuring the physical properties of dielectric materials, and, more particularly, it relates to apparatus for measuring the moisture content of moving dielectric materials, such as a paper web, woven cloth, etc.
There exists apparatuses for measuring the moisture content of moving dielectric materials, e.g. of a moving paper web, having their operation based on determining the intensity of the electromagnetic radiation created by electric discharges occuring between the moving paper web and the associated machinery on account of adhesion and friction therebetween.
These apparatuses of the prior art comprise means adapted to receive directly the electric signals carrying information representative of the moisture content of the moving dielectric material and to transmit these signals to electric measuring systems for converting the values of these signals into values proportional to the moisture content of the moving dielectric material.
The abovementioned means in known apparatus includes aerials adapted to receive the electromagnetic field of radiation, whereas the electric measuring system includes a band-pass tuned filter, an amplifier, a detector and a registering device, connected in series.
The apparatus of the prior art is equipped with an inverted scale wherein the zero reading is at the extreme right, which complicates the recording of the readings, since the readings are to be calculated from the right to the left when the apparatus is operated in a registration mode. Furthermore, the known apparatus cannot be incorporated in an automatic control system, both on account of its inverted scale and of its propensity to produce a false signal should the moving material break. In such a case, when actually the material is not advanced, the pointer of the registering device is in its extreme left position which is an indication of a maximum moisture content, e.g. of the necessity to add steam to the drying unit, whereas in fact it is necessary to reduce the steam supply.
Moreover, to ensure normal operation of the apparatus, both when it is operated in a registration mode and when it is incorporated in an automatic control system, there should be provided registration of an overload condition of the registering device, should an excessively great signal be applied to the input of the apparatus.